Yes, the Conservative Party manifesto of 2017 did both rule out continued membership of the Single Market and the Customs Union but it did then say, as Paul quoted, that the UK would seek a deep and special partnership via a free trade and customs agreement.

It could be argued, although I don’t buy it, that this manifesto pledge doesn’t stand because the Conservative Party did not gain a majority in the Commons in last year’s election. After all, other policies contained in that manifesto will never be put to the Commons because the Government knows there is no mandate and no majority for them.

Instead my alternative argument to Paul, which is more likely to result in a compromise which all Conservative MPs can support, is to explore what is mean by a ‘customs agreement’.

And one of the ways to tease out what might be meant is to look back to the Prime Minister’s Lancaster House speech last January. This is the speech mentioned several times, approvingly, by 62 of my colleagues in a letter to the Prime Minister last week (whereas the later Florence Speech of last year was ignored).

In that Lancaster House speech the Prime Minister said,

“I know my emphasis on striking trade agreements with countries outside Europe has led to questions about whether Britain seeks to remain a member of the EU’s Customs Union. And it is true that full Customs Union membership prevents us from negotiating our own comprehensive trade deals.

Now, I want Britain to be able to negotiate its own trade agreements. But I also want tariff-free trade with Europe and cross-border trade there to be as frictionless as possible.

That means I do not want Britain to be part of the Common Commercial Policy and I do not want us to be bound by the Common External Tariff. These are the elements of the Customs Union that prevent us from striking our own comprehensive trade agreements with other countries. But I do want us to have a customs agreement with the EU.

Whether that means we must reach a completely new customs agreement, become an associate member of the Customs Union in some way, or remain a signatory to some elements of it, I hold no preconceived position. I have an open mind on how we do it. It is not the means that matter, but the ends.

And those ends are clear: I want to remove as many barriers to trade as possible. And I want Britain to be free to establish our own tariff schedules at the World Trade Organisation, meaning we can reach new trade agreements not just with the European Union but with old friends and new allies from outside Europe too”.

As Turkey shows us, a customs union deal with a non-EU member is possible. If the Government is determined to pursue a bespoke end-state agreement with the EU then an imaginative customs union agreement which means no hard border between Northern Ireland and the Republic of Ireland is perfectly possible. And it is something our sovereign Parliament should be discussing.

Downing Street’s first briefing this weekend in response to a proposed New Clause Five to the Trade Bill was the right one – that those who have concerns about leaving the customs union with the EU should listen to what the Prime Minister will say at the end of this week. The test for that speech is how much further on it gets us 13 months after the Lancaster House speech.

The next briefing, that any vote on such an amendment should be regarded as a confidence motion, unnecessarily raises the temperature between Ministers and the Conservative Parliamentary Party. If every amendment to the Brexit Bills becomes a confidence issue, we are in for an even more disruptive few months than the Whips office currently predict.

Finally, let’s not forget partisan politics in this. Labour are apparently now committing to the UK being in some form of treaty which “does the work of the customs union”. If confirmed then, as demonstrated above, they are playing catch up with the Conservative Government and MPs who’d already in 2017 reached the conclusion – according to the Lancaster House speech and our manifesto – that some form of “completely new customs agreement … associate member[ship] of the Customs Union in some way, or remain[ing] a signatory to some elements of it” has to happen.

When we reach the Trade Bill, New Clause Five will allow us to probe (assuming we don’t already have the answers from the Prime Minister), how the Government intends to reflect those words in our negotiations with the EU for a future trade agreement.